Linking error after `dune build @site`: undefined reference to `core_unix_gettid'

[Kakadu]

...
Generating variables-and-functions.html...
File "bin/bin/dune", line 3, characters 15-18:
3 |  (names        app convert_md)
                   ^^^
/usr/bin/ld: duniverse/core_unix/linux_ext/src/linux_ext.a(linux_ext.o): in function `camlLinux_ext__sched_setaffinity_this_thread_6567':
/media/oldwork/asp/book/_build/default/duniverse/core_unix/linux_ext/src/linux_ext.ml:830:(.text+0x4b00): undefined reference to `core_unix_gettid'
/usr/bin/ld: duniverse/core_unix/linux_ext/src/linux_ext.a(linux_ext.o): in function `camlLinux_ext__const_immstring_195':
:(.data+0x5758): undefined reference to `core_unix_gettid'
collect2: error: ld returned 1 exit status
File "caml_startup", line 1:
Error: Error during linking (exit code 1)   

[juergenhoetzel]

See: janestreet/jst-config#5

I pinned and cherry-picked the fix to get around this issue:

git checkout v0.14.1
git cherry-pick a5cddd0e657b9fc3f6775da8ebdaa6d25446b649
opam pin .